Add linked doi

cf. E-DataPortal#625 (closed)
We could add in the json datacite the list of the related dois: a dataset of teh session which is referenced in a dataCollection
It could be added as a relatedIdentifier with the relationType isSupplementedBy:

<relatedIdentifier relatedIdentifierType="DOI"
relationType="IsSupplementedBy">10.151/ESRF-DC-XXXX
</relatedIdentifier>